Encryption systems are used in a variety of applications, and prevent sensitive data from being compromised. Encryption systems often rely upon a key or other secure value that is used to encrypt data or otherwise prevent access to data by an unauthorized user. Entropy is a measure of randomness in a system, where a high level of entropy associated with a value used to generate a key or other secure value can be significant in an encryption system or any system requiring a random value. A physically unclonable function (PUF) is one type of system generating a random number. A PUF enables providing a unique signature or fingerprint for a given integrated circuit. This signature or fingerprint is different from device to device, where the different devices may include die from the same wafer. A useful PUF provides stable uniqueness without bias or aging effects. This uniqueness may be based upon physical variations to produce differences between circuit elements.
Accordingly, methods and circuits that improve the security of values used in a secure system are beneficial.